X-ray computer tomography, ultrasonic computer tomography and MRI are well known methods for localizing objects in a turbid medium, especially for the localization of breast cancer and tumors. Optical computer tomography uses the fact, that near infrared light exhibits a high transmissivity with respect to biological tissues and growth of tumors or cancer can be monitored by a characteristic absorption of light in breast tissue. An advantage for using an optical computer tomography device is also, that special contrast agents with fluorescent tags can be used, in order to localize cancer areas in breast tissue. The fluorescent contrast agent is thereby adapted to accumulate in the cancer area. Consequently, the cancer area labeled with the contrast agent emanates a characteristic fluorescing light upon irradiation with a laser at a certain wavelength or upon irradiation with a light source of certain bandwidth.
Typical devices for localizing an object in a turbid medium can be seen in U.S. Pat. No. 6,687,532 B2. A common disadvantage using an optical computer tomography apparatus is, that the dynamic range of the intensity of the light emanating from the irradiated turbid medium is rather large. Therefore, respective photo detectors have to cover a large dynamic sensitivity range. This necessitates complex and rather expensive electronics. Furthermore, for diffuse optical fluorescence measurements, the optical fluorescence signal from the turbid medium is typically very small and an up to 100 times larger transmission contribution has to be measured at the same time together with the small fluorescent signal. This again necessitates complex and expensive optics with large dynamic range photo detectors of precisely defined spectral range.